1. Field of the Invention
The present invention relates to a method and apparatus for image forming and effectively applying lubricant to an image bearing member. More specifically, the present invention relates to a lubricant supplying device that can effectively apply lubricant, an image forming apparatus using a method of electrophotography, electrostatic recording, and electrostatic printing, and including the lubricant supplying device, and a process cartridge included in the image forming apparatus.
2. Discussion of the Related Art
Recently, there has been a strong demand for image forming apparatuses using an electrostatic copying method having a higher productivity of images. While means and methods for obtaining higher productivity of images is studied, toner is also being studied to obtain increased sphericity and smaller particle diameter in order to form high definition images. As toner prepared by pulverizing methods are limited with regard to these properties, polymerized toner prepared by suspension polymerizing methods, emulsification polymerizing methods, and dispersion polymerizing methods for conglobating the toner and making toner having a small particle diameter are being used.
Toner of this nature having a substantially spherical shape, however, have poor cleaning ability. Background image forming apparatuses have used a cleaning device with a cleaning blade for removing toner produced using a pulverizing method. The cleaning blade is held in contact with a surface of a photoconductive element that serves as an image bearing member so that the cleaning blade can scrape toner remaining on the surface of the photoconductive element. However, the cleaning blade cannot stop small toner having a substantially spherical shape from falling through a space between the image bearing member and the cleaning blade into the interior of the image forming apparatus. To remove the toner having the substantial spherical shape, lubricant is applied to a surface of the image bearing member to reduce a coefficient of friction of the image bearing member so that the friction between the image bearing member and the toner is reduced, resulting in easy removal of the toner from the surface of the image bearing member.
To contact the cleaning blade with the surface of the photoconductive element, a predetermined amount of pressure is applied to the cleaning blade. When the pressure is applied for a long period, toner, external additives of toner, and/or hazardous products such as Nox can cause adhesion (or filming) to the surface of the image bearing member, resulting in an image defect such as image deletion. To avoid the above-described condition, the coefficient of friction of the image bearing member is sufficiently reduced, and it is result effective that a lubricant is applied onto the surface of the image bearing member.
A charging device of a background image forming apparatus charges the image bearing member employing a charging method such as a corotron or scrotron method using corona, for example, which is referred to as a corona discharge method. Recently, however, a charging method, in which a charging roller is held in contact with the image bearing member or is disposed in a vicinity of the image bearing member, has been increasingly used in view of environmental circumstances. In the charging method with the charging roller held in contact with the image bearing member or disposed in a vicinity of the image bearing member, a direct-current voltage superimposed with an alternating-current voltage is applied to obtain better uniform charging ability. The direct-current voltage, however, can produce a rough surface on the image bearing member. This tends to increase a coefficient of friction of the image bearing member, which can make the above-described problem more pronounced. According to the above-described circumstances, it is more important that when an image forming apparatus has a charging device to charge the surface of an image bearing member with a direct-current voltage superimposed with an alternating-current voltage, a lubricant is applied to the surface of the image bearing member so that the coefficient of friction can be reduced.
A commonly known lubricant supplying device uses a molded lubricant that includes zinc stearate in a solid form and a brush roller that simultaneously contacts the molded lubricant and the photoconductive element and rotates in a predetermined direction.
A technique has been proposed where a brush roller serves as a lubricant supplying device. In the technique, the brush roller includes a fibrous brush of a thickness of approximately 7.5 deniers to approximately 15 deniers in a circumference of its rotative supporting axis with a density of approximately 20,000 fibers to approximately 60,000 fibers per square inch. The molded lubricant used in the lubricant supplying device has a hardness of pencil such as “H” for “hard”, “F” for “firm”, “B” for “black”, and “HB” for “hard black” and is held in contact with the brush roller at a pressure equal to or less than 1.18 N/m. The lubricant supplying device is used to minimize the consumption of the molded lubricant, is provided in a simple mechanism, and maintains lubrication for a long period of time.
In recent years, inorganic fine particles have been added externally to toner to improve cleaning ability. The inorganic fine particles, however, can adhere to the surface of the image bearing member, cause a filming, and result in an image defect. As previously described, in order to prevent the filming, it is effective to apply the lubricant made of zinc stearate onto the surface of the image bearing member. When a new unit of an image bearing member is used, a new lubricant is also provided and the surface of the lubricant is covered with a skin layer. In this condition, the brush roller cannot easily scrape the molded lubricant, and the amount of the molded lubricant to be supplied becomes low, which can cause the filming. Increasing the amount of pressure applied by the molded lubricant on the brush roller can solve the above-described problem, and can supply a predetermined amount of the molded lubricant. As time passes on, however, the amount of the molded lubricant supplied becomes excessive, which can cause contamination of a charging roller, clogging of used toner due to its low flowability, reduction of the lifespan of the molded lubricant, and so on.
Another technique has been proposed where a lubricant supplying device maintains a coefficient of friction “μ” at a predetermined value by applying a solid lubricant onto a surface of an image bearing member. However, such a technique cannot eliminate the problem described above.
As described above, applying a lubricant onto a surface of an image bearing member and reducing the coefficient of friction of the image bearing member can maintain good cleaning availability and sharply reduce a chance of filming. However, an excessive amount of the lubricant can cause an image defect and a short life of the image forming apparatus. When the molded lubricant is too hard, an extra force for the brush roller to scrape the molded lubricant is required. When the force to be exerted to scrape the molded lubricant is increased, the force is likely to break the molded lubricant and/or make the fibers of the fibrous brush tilt. Consequently, an appropriate lubrication may not be applied and cause an image defect.
When a simple compressed spring is used as a pressuring member, a spring constant increases, which can cause a difference between the initial value and the aged value. This may vary the amount of lubricant due to aging.
When the molded lubricant is too soft, the molded lubricant can break during machine operation, manufacturing process, secondary fabrication, and/or transportation. Further, the amount of lubricant is likely to become greater.